Ion source



,Jan. 29, 1963 M. WASSERMAN ION SOURCE 2 Sheets-Sheet 1 Filed Jan. 18,1960 ATTORNEYS Jan. 29, 1963 M. WASSERMAN ,112

ION SOURCE Filed Jan. 18, 1960 2 Sheets-Sheet 2 IMVENTOR M. WAJ'SERMA/VATTO NEY M 4 $5 +r 2 72% T..

aired tee l stens 3,076,112 N SQURCE Marian Wasserznan, Paris, France,assignor to (Iompaguie Generals do Telegraphic liens Fil, Paris, FranceFiled Jan. 13, 19st), tier. No. 2,877 Claims priority, applicationFrance Feb. 2, 1.959 iliainis. (Cl. 313-63) The present inventionrelates to an apparatus constituting an ion source, and moreparticularly relates to an ion source apparatus producing a hollow ionbeam for use in connection with utilization devices in which a magneticfield having a circular symmetry is used.

Utilization devices for ionized gases are known in the prior art inwhich the ions have to be placed into a magnetic field with circularsymmetry which may be produced, as known, by the flow of an intensecurrent through an axial metallic rod or conductor. When an injection ofthe ions in the sense of this sleeve or conductor is desired withsimultaneous preservation of the conditions of symmetry thereof, it isnecessary that the ion source produces a hollow beam having as its axisthe metallic rod or conductor in question. While ion guns are known inthe prior art which produce ion beams of either full cylindricalconfiguration or plane configuration, none of the prior art ion sourcesis suitable for the injection of ions into a utilization device or" atype described hereinabove, which requires a hollow ion beam of circularsymmetry.

The present invention has for its principal object to provide a sourcefurnishing a hollow ion beam which is injected into the utilizationvessel or enclosure both axially and symmetrically about the central rodor conductor of this vessel, whereby the rod or conductor is traversedby a current generating the magnetic field having lines of force withcircular symmetry.

The ion source according to the present invention belongs generally tothe type in which the ionizing electrons move in mutually crossedelectric and ma netic fields, as described for example in the UnitedStates Patent 2,935,- 634, filed on lune 13, 1957, in the name of A.Lerbs and assigned to the assignee of the present invention which patentdescribes a source providing a plane ion beam.

Accordingly, it is an object of the present invention to provide an ionsource for use with load or utilization devices of the type describedhereinabove which obviates the disadvantages and shortcomings of theprior art devices.

It is another object of the present invention to provide an ion sourcewhich produces a fully satisfactory, hollow ion beam by relativelysimple means.

Another object of the present invention resides in the provision of anion source producing a hollow circular ion beam which may be used withina utilization enclosure or vessel in which a magnetic field withcircular symmetry is established.

T ese and other objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing, which shows, forpurposes of illustration only, two embodiments in accordance wit thepresent invntion and wherein:

FEGURE l is an axial, longitudinal cross-sectional view of a firstembodiment of an ion source in accordance with the present invention,and

FIGURE 2 is an axial, longitudinal cross-sectional view through amodified embodiment of an ion source in accordance with the presentinvention.

The present invention is characterized by the fact that the ion sourcecomprises an electron-optical and ionic system of electrodes withsymmetry of revolution about the magnetic-field-producing axial rod orconductor, and that not only the ionizing electrons but also the wasleaving the ionization space move within crossed electric and magneticfields, established within a cylindrical space comprised between theelectrode for the extraction of the ions and the axial rod or conductorin such a manner that the ions are concentrated or focused into a hollowbeam within this space.

Referring now to the drawing, wherein like reference numerals are usedthroughout the two views to designate corresponding parts, and moreparticularly to FIGURE 1, reference numeral 1 designates therein an ionstabilization vessel or enclosure which is defined or limited by thewalls 2 and includes within the axis thereof a metallic rod or conductorA source of current supply 4, which is connected between the ends of therod 3, sends current therethrough in the direction indicated in PEGURE lby the arrow, that is, from the right to the left as viewed in FIGURE 1,which establishes a magnetic field with the circular lines of forceabout the axis, this field being directed toward the plane of thedrawing in the upper part of the cross-sectional view of FIGURE 1 andtoward the observer or viewer in the lower part thereof, as indicatedalso by the encircled small cross and dot, respectively, and designatedby reference character B.

The vessel or enclosure 1 is supplied with ions from the left thereof bymeans of an ion source constructed in accordance with the presentinvention. This ion source cornprises an electrode system including acathode electrode in the form of two cylinders 5- and 6, separated by agap 7; an ion extraction electrode in the form of two cylinders S andseparated by a gap lb and disposed between the cylinders 57 and 6 andaxial rod 3; an annular cathode 11, supported on the cylinder 5; anelectron-optical or focusing anode in the form of a cylinder 12, facingthe cathode ll; and an anode electrode in the form of a cylinder 13,surrounding the cylinders 5 and 6. All of these electrodes have asymmetry of revolution about rod 3.

The electrodes 12 and 13, for example, are incorporated into the walls14 of the glass vessel or enclosure which contains the gun and whichbelongs to the enclosure or vessel 1. This vessel is closed by anannular member 15 made of Kovar, secured to the ring member 16 which isadapted to slide along the rod- 3. The ring member 36 is connected bymeans of bellows 1'7 made of tombac to a boss 13 provided on the rod 3.in that manner, the rod 3 may expand freely without damaging the glassstructure M.

The electrodes 5 and a are interconnected with each other in anysuitable manner and are also connected to a positive potential withrespect to the rod 3. The cathode ll, supplied from a source notillustrated, is also connected to the potential of electrode 5. Theanodes l2 and 13 are carried at suitable positive potentials withrespect to electrodes 5 and 6 by means of source 19. The electrodes 8and 9 are interconnected in any suitable manner and are also carried ata potential suitably chosen intermediate that of the rod 3 and that ofelectrodes 5 and 6 by means of the same source 19.

A tubular channel 2%? discharges through electrode 13 to permit theadmission of a gas under slight pressure to be ionized. A tubular member21, connected to a suitable vacuum pump (not illustrated herein)terminates through wall 14 to permit evacuation and therewith theestablishment of a vacuum within a portion of the gun enclosure orvessel. This intercornrnunication between the portion in which prevailsthe slight gaseous pressure and the portion in which the vacuum prevailsis essentia ly precluded almost completely, on the one hand, by an endcover 22 formed by cylinder 5 and provided in the center thereof with anaperture just sufficiently Ii large to permit passage therethrough ofrod 3 and, on the other, by an end cover 23 formed by cylinder 13 andprovided in the center thereof with an aperture suificient to permit thepassage therethrough of the cathode cylinder 5 and includingadditionally an annular gap 24 intended for the passage of theelectrons. Another end cover of the same cylinder 13 serves as collectorfor the electrons.

Operation The operation of the device illustrated in FIGURE 1 is asfollows:

When the particular voltages are applied to the various electrodes andcurrent flows through rod 3, the electrons emitted from the cathode 11,under the effect of the radial electric field established between theelectrode 12 and the electrode 5, and of the transverse magneti: fieldcaused by the how of current through rod 3, follow urved paths ortrajectories 26. These paths or trajectories 20' enter through the gap24 into the space comprised between electrodes 13 and 5, 6 in whichelectrons move from the left to the right, as viewed in FIGURE 1, andparallelly to the rod 3 by the action of the same magnetic field or"which the direction is indicated by the circles B, crossed with theradial electric field directed from the interior toward the exteriorthereof, and established between electrodes 13 and 5 or 6. The parallelelectron paths define a cylindrical pattern of the ionizing beam whichis coaxial with the rod 3. The electron paths pass through what are inefiect a plurality of ionizing areas located at difierent angularlyspaced points around the rod 3, these ionizing areas combining with eachother to form an ionizing chamber completely encircling the rod 3. Atthe end of the electron fiow, the electrons are captured by collector2.5.

The gas emitted into the same space through tubular member 2% is ionizedby these electrons. The positive ions are attracted by the negativeextraction electrode 8, 9 and leave the ionization space throughsuccessive gaps 7 and 16.

According to the particular feature of the present invention, the ionswhich leave through gap 10 find themselves anew within the mutualcrossed electric and magnetic fields, these fields being establishedbetween the cylindrical space between the extraction electrode 8, 9 andthe rod 3. The transverse magnetic field and the radial electric fieldhave here the same direction as in the ionization space. The electricfield, in effect, is directed from the interior toward the exterior,thanks to the difference of potential between electrodes 3 and 8 or 9.It is known that when neither the direction of the magnetic field northat of the electric field changes, the ions move in the same axialdirection as the electrons of the beam 26. Consequently, the ionseventually move in parallel paths and are concentrated into a hollowbeam 27 directed from the left to the right as viewed in the drawing andare thereupon injected into the enclosure 1. The parallel paths of theions define a cylindrical pattern of the ion beam which is also coaxialwith the rod 3.

The embodiment illustrated in FIGURE 2 in which the same parts aredesignated by identical reference numerals as in FIGURE 1 discloses anarrangement in which the current in rod 3 has been reversed with respectto that of FIGURE 1.

Consequently, in the embodiment of FIGURE 2, the magnetic field haschanged its direction and is directed toward the observer in the upperportion of the crosssectional View of the drawing, and toward the planeof the paper in the lower portion thereof. Under these conditions, withthe electric field within the ionization space remaining directed fromthe interior toward the exterior, the movement of the electrons whichionize the gas changes its direction, and is directed from right to leftas viewed in FIGURE 2. The arrangement of the electrodes within theionization space is therefore modified in FIGURE 2 by placing thecathode 11 and the focusing anode 12 toward the right, and the cylinder13 with the collector 25 toward the left thereof. Furthermore, theelectrodes 8, 9 are now carried at a negative potential with respect torod 3. Consequently, the electric field within the space between theseelectrodes 8, 9 and rod 3 is directed from the outside toward theinside, and is, therefore, inverse with respect to the electric fieldwithin the ionization space. Thanks to this simultaneous inversion ofthe magnetic field and of the electric field with respect to theconditions of FIGURE 1, the ion beam 27 moves in FIGURE 2 in the samedirection as in FIGURE 1, and in the opposite direction with respect tothe flow of electrons in FIGURE 2, that is, from left to right as viewedin FIGURE 2. Otherwise, the operation of the device shown in FIGURE 2 isthe same as that of FIGURE 1.

While I have shown and described'two embodiments in accordance with thepresent invention, it is understood that the same is not limited theretobut is susceptible of many changes and modifications within the spiritand scope of the present invention, and I, therefore, do not Wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

I claim:

1. In a rotational symmetry device traversed along its axis by a metalrod and having feeding means for said rod to send an electric currenttherethrough, thereby gen erating magnetic field having lines of forceof circular shape around said rod, an ion source having a cylindricalextraction electrode coaxial with said rod, an evacuated vesselsurrounding said electrode, means for feeding gas to be ionized intosaid vessel, means for emitting a hollow electron beam propagatingsubstantially parallel to said rod through said gas thereby ionizing itincluding first radial electric field generating means acting togetherwith said circular magnetic field on said electrons to direct the samesubstantially perpendicularly to both said fields, and means forgenerating a second radial electric field in the space between said rodand said extraction electrode, said last-mentioned space receiving ionsproduced by said ionizing electrons and extracted through saidextraction electrode, and said circular magnetic field acting on saidions to concentrate said ions into a hollow tubular beam propagating insaid space substantailly parallel to said.

rod' and substantially perpendicular to both said lastmentioned fields.

2. An ion source as claimed in claim 1, wherein both said first andsecond radial electric fields are of the same sense, and both saidelectron and ion beams are propagating in the same direction.

3. An ion source as claimed in claim 1, wherein both said first andsecond radial electric fields are of opposed sense, and both saidelectron and ion beams are propagating in opposed directions.

4. An ion source having an ionization space for producing a hollow ionbeam, comprising means for establishing crossed magnetic and electricfields in said space with the magnetic field being generally circularabout a predetermined axis and the electric field being radial withrespect to said axis, gas supply means for supplying a gaseous mediumadapted to be ionized by an electron beam generally encircling said axiswithin said ionization space, and means including said first-mentionedmeans for producing said ionizing electron beam and for extracting theions created by the said ionizing electron beam in the form of a hollowcylindrical ion beam encircling said axis.

5. An ion source having a generally annular ionization space forproducing a hollow ion beam, comprising means for establishing crossedmagnetic and electric fields in said space including axial conductormeans through which current fiows for setting up a circular magneticfield thereabout, gas supply means for supplying a gaseous mediumadapted to be ionized by an electron beam Within said ionization space,means including said first-mentioned means for producing said ionizingelectron beam, and means including electrode means in combination withsaid first-mentioned means for directing the ions produced by the saidionizing electron beam in such a manner that the ions move in the formof a hollow cylindrical ion beam encircling said conductor within saidcrossed electric and magnetic fields.

6. An ion source according to claim 5, wherein said electric field is aradial field.

7. An ion source having an ionization space for producing a hollow ionbeam, comprising means for establishing crossed magnetic and electricfields in said space including axial conductor means through whichcurrent passes for setting up a circular magnetic field thereabout, gassupply means for supplying a gaseous medium adapted to be ionized by anionizing electron beam within said ionization space, electron emissivemeans for emitting an ionizing electron beam guided by saidfirst-mentioned means and encircling said conductor in said space, andmeans including said first-mentioned means and additional electrodemeans for establishing a second electric field to focus and guide saidions produced in said space by the said ionizing electron beam in such amanner that the ions move in the form of a hollow cylindrical ion beamencircling said conductor within said crossed electric and magneticfields.

8. An ion source according to claim 7, wherein both of said electricfields are radial fields.

9. An ion source having an ionization space for producing a hollow ionbeam, comprising means for establishing crossed magnetic and electricfields including axial conductor means through which current passes forsetting up a circular magnetic field thereabout and electrode meanshaving a symmetry of revolution about said conductor means forestablishing at least one electric field, gas supply means for supplyinga gaseous medium adapted to be ionized by an ionizing electron beamwithin said ionization space, and means for producing said electron beampropagating within said fields, the ions produced by said ionizingelectron beam also propagating within said fields and being focusedthereby into a hollow cylindrical ion beam within said crossed electricand magnetic fields.

10. An ion source according to claim 9, wherein said electrode meansestablish two electric fields.

11. An ion source according to claim 10, wherein said electric fieldsextend essentially radially.

12. An ion source having an ionization space for producing a hollow ionbeam by the interaction with a gaseous medium of the electrons in anelectron beam propagating within crossed magnetic and electric fields,comprising axial conductor means through which current passes forsetting up said magnetic field having a circular configurationthereabout, gas supply means for introducing a gaseous medium to beionized into said ionization space, and electron-optical electrode meansgenerally encircling said conductor means for establishing said electricfield and for extracting the ions produced by the said ionizing electronbeam from said ionizing space and pro pagating the same in the form of ahollow cylindrical ion beam within said crossed electric and magneticfields.

13. An ion source for producing a hollow ion beam comprising means forproducing a generally cylindrical ionizing electron beam including meansfor establishing crossed magnetic and electric fields for guiding saidelectron beam, said last-rnentioned means including an axial conductorthrough which current passes for setting up the magnetic field ascircular thereabout, gas supply means for introducing a gaseous mediumto be ionized into said ionization space, an electrode means forfocusing and separately grouping said electrons and ions in such amanner that the ions produced by said ionizing electrons move alsoWithin said crossed electric and magnetic fields in the form of a hollowcylinder.

14. An ion source having an ionization space for producing a hollow ionbeam by the interaction with a gaseous medium of the electrons in anelectron beam propagating within crossed magnetic and electric fields,comprising axial conductor means through which current passes forsetting up said magnetic field having a circular configurationthereabout, electron-optical electrode means for establishing saidelectric field and for extracting the ions produced by the said ionizingelectron beam from said ionizing space and propagating the same in theform of a hollow cylindrical ion beam within said crossed electric andmagnetic fields, said electrode means including two concentric electrodesystems disposed about said conductor means, and means for establishinga first electric field between said two electrode systems and a secondelectric field in the space between the inter electrode system and saidconductor means.

15. An ion source for producing ions propagating in parallel pathsgenerally defining a cylindrical pattern, comprising means forestablishing crossed magnetic and electric fields at ionizing areaslocated at difierent angularly spaced points around the axis of saidcylindrical pattern, said last-mentioned means including a conductorextending coaxially of said cylindrical pattern and means for passing acurrent through said conductor for establishing said magnetic field as acircular field thereabout, means for supplying an ionizable medium tothe ionizing areas in said crossed fields, and means including saidcrossed field establishing means for producing ionizing electrons movingin said ionizing areas parallel to said conductor to ionize saidionizable medium, and means including electrode means in combinationwith said firstmentioned crossed field establishing means for separatingions from said ionizing electron for propagating said ions in saidparallel paths along said cylindrical pattern.

References Cited in the file of this patent UNITED STATES PATENTS2,760,101 Reverdin Aug. 21, 1956 2,761,088 Warnecke et a1. Aug. 28, 19562,935,634 Lerbs May 3, 1960

1. IN A ROTATIONAL SYMMETRY DEVICE TRAVERSED ALONG ITS AXIS BY A METALROD AND HAVING FEEDING MEANS FOR SAID ROD TO SEND AN ELECTRIC CURRENTTHERETHROUGH, THEREBY GENERATING MAGNETIC FIELD HAVING LINES OF FORCE OFCIRCULAR SHAPE AROUND SAID ROD, AN ION SOURCE HAVING A CYLINDRICALEXTRACTION ELECTRODE COAXIAL WITH SAID ROD, AN EVACUATED VESSELSURROUNDING SAID ELECTRODE, MEANS FOR FEEDING GAS TO BE IONIZED INTOSAID VESSEL, MEANS FOR EMITTING A HOLLOW ELECTRON BEAM PROPAGATINGSUBSTANTIALLY PARALLEL TO SAID ROD THROUGH SAID GAS THEREBY IONIZING ITINCLUDING FIRST RADIAL ELECTRIC FIELD GENERATING MEANS ACTING TOGETHERWITH SAID CIRCULAR MAGNETIC FIELD ON SAID ELECTRONS TO DIRECT THE SAMESUBSTANTIALLY PERPENDICULARLY TO BOTH SAID FIELDS, AND MEANS FORGENERATING A SECOND RADIAL ELECTRIC FIELD IN THE SPACE BETWEEN SAID RODAND SAID EXTRACTION ELECTRODE, SAID LAST-MENTIONED SPACE RECEIVING IONSPRODUCED BY SAID